Phase change compositions

ABSTRACT

Compositions containing crystalline, straight chain, alkyl hydrocarbons as phase change materials including cementitious compositions containing the alkyl hydrocarbons neat or in pellets or granules formed by incorporating the alkyl hydrocarbons in polymers or rubbers; and polymeric or elastomeric compositions containing alkyl hydrocarbons.

GOVERNMENT RIGHTS

The U.S. Government has certain rights under the inventions disclosedherein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.935,081, filed Nov. 24, 1986, now abandoned, which is acontinuation-in-part of U.S. application Ser. No. 835,418, filed Mar. 3,1986, now abandoned, which is a continuation-in-part of U.S. applicationSer. No. 646,402, filed Aug. 31, 1984, now U.S. Pat. No. 4,617,322.

BACKGROUND OF THE INVENTION

The present invention relates to compositions embodying phase changematerials and, more particularly, to compositions containingcrystalline, long chain alkyl hydrocarbons having at least 14 carbonatoms.

There is a great deal of interest in phase change thermal energy storagesystems due to their inherent ability to store large amounts of heat andrelease it to the surrounding environment as temperatures drop below orexceed predetermined levels. These systems are of particular interest inthe architectural and building trades where climate control and itsconcomitant energy consumption is one of the principal considerations inbuilding design and material selection.

A variety of building materials and techniques have previously been usedto conserve heat or cool and thereby reduce energy costs. Included amongthem are structural elements which incorporate phase change materials.By incorporating phase change materials into building materials, energyin excess of that necessary to maintain comfort conditions is inherentlyabsorbed and released as required to maintain the comfort range. Thus,in winter months, phase change materials incorporated into structuralelements in the walls or floors of buildings and the like can absorbsolar energy during daytime hours and release it to the interior atnight as temperatures drop. In summer months, the same phase changematerial, due to its thermostatic character, conserves coolness byabsorbing energy.

Structural elements incorporating phase change materials are moredesirable than elements which store only sensible heat because they havea higher capacity to store energy and they absorb and release a largequantum of energy over a very narrow temperature range. A phase changematerial utilizes its latent heat of fusion as well as its sensible heatcapacity for thermal storage. The latent heat of fusion is substantiallygreater than the sensible heat capacity of the material. That is, theamount of energy a material absorbs upon melting, or releases uponfreezing, is much greater than the amount of energy it absorbs orreleases upon increasing or decreasing in temperature 1° C. Thus, uponmelting and freezing, per unit weight, a phase change material absorbsand releases substantially more energy than a sensible heat storagematerial which is heated or cooled through the same temperature range.Furthermore, as contrasted with a sensible heat storage material whichabsorbs and releases energy essentially uniformly over a broadtemperature range, a phase change material absorbs and releases a largequantum of energy in the vicinity of its melting/freezing point. This isparticularly advantageous in buildings where space is at a premium andenergy storage and release are required within a very narrow comfortrange.

It has long been recognized that an effective phase change material,which could store and release thermal energy within the temperaturerange of 10°-65° C. and could be economically incorporated into commonbuilding materials (e.g. concrete, cement, plaster, rubber, plastics),would have broad utility for many heating and cooling applicationsincluding solar passive, solar active, off-peak electric load leveling,bridge deck deicing, etc. Other types of phase change materials havebeen investigated that melt and freeze in the above temperature range,and have a high heat of fusion (e.g., salt hydrates and clathrates); butwidespread use has not been achieved because of the difficulty ofcontainerizing them, their instability to repeated thermocycling,corrosion, leakage, etc.

Paraffin waxes have been considered for use in building materials asphase change materials but until now effective methods of incorporatingthem into building materials were not available and/or they involvedprohibitive loss in the physical properties of the building materials.

Among the teachings which were available in the art prior to the presentinvention are those of U.S. Pat. No. 4,259,401 to Chahroudi et al whichdiscloses both structural and non-structural building materialsincorporating phase change materials. These building materials are madeup of a rigid porous matrix structure which is impregnated with thephase change material. Three classes of phase change materials aredisclosed, namely, hydrated salts, waxes, and clathrates. Cements,plasters or thermosetting materials may form the rigid matrix.

U.S. Pat. No. 4,504,402 to Chen teaches an encapsulated phase changematerial which is prepared by forming a shell about a phase changecomposition in compacted powder form. One of the applications of theencapsulated phase change materials is in concrete or gypsum structures.

SUMMARY OF THE INVENTION

The present invention is broadly directed to compositions which areuseful in thermal energy storage and include crystalline, long chain,alkyl hydrocarbons having 14 or more carbon atoms, as phase changematerials.

Crystalline alkyl hydrocarbon are particularly advantageous phase changematerials. The melting temperature of the paraffins increases until a"limiting" melting point of about 130° C. is reached in products havingmore than 40 carbon atoms in an unbranched chain. Consequently, one canselect a crystalline hydrocarbon of any desired melting temperaturebetween 0° and 80° C. for use as a phase change material for solaractive and passive applications. Depending on the purity of thecompounds, heats of fusion range from about 40 to 60 cal/gm. Thecompounds are non-toxic, non-corrosive and non-hygroscopic andinexpensive. At the same time, they are fairly resistant to thermalcycling.

It has been found that alkyl hydrocarbons are particularly useful in theform of blends of two or more crystalline alkyl hydrocarbons. Moreparticularly, it has been found that crystalline alkyl hydrocarbonblends obtained at low cost as byproducts of petroleum refiningoperations are economically advantageous for use in the presentinvention. Depending on the difference in the melting points of theconstituents of the blend, the blend exhibits thermal storagecharacteristics intermediate those of the individual alkyl hydrocarbonswithout a decrease in heat of fusion.

By choosing the proper alkyl hydrocarbons, the temperature at whichthermal energy is stored can be varied from -12° C. (tetradecane) to 95°C. (commercial microcrystalline waxes). For bridge deck deicing,hexadecane, which melts at about 10° C., is advantageous. For solarpassive applications in climate control octadecane, which melts at about28° C., is used. For solar active storage applications commercialparaffin waxes which melt in the range of 50°-65° C. are desirable.

In accordance with one embodiment of the present invention, crystalline,alkyl hydrocarbons are incorporated into polymeric or inorganiccementitious compositions such as hydraulic cements.

It has been found that alkyl hydrocarbons can be directly incorporated,by dry or wet mixing, into hydraulic cementitious compositions such asconcrete, cement and plaster, at concentrations up to 10 percent byweight in the case of certain cements and 10 to 20 percent by weight inthe case of gypsum, without prohibitive loss in the strength propertiesof the matrix. In accordance with more preferred embodiments of theinvention alkyl hydrocarbons are pre-mixed with an absorptive filler orincorporated into a hard wax, or rubber or plastic pellet, forincorporation into inorganic cementitious mixes.

In accordance with another embodiment of the present invention, certainflame-resistant agents are used in combination with the crystallinealkyl hydrocarbons to confer flame retardancy. Certain halogenatedhydrocarbons are useful for this purpose. These hydrocarbons arepreferably used with a polyvalent metal oxide such antimony oxide, whichreacts with the halogen liberated upon combustion and generates a densesnuffing gas.

In another embodiment of the invention, the alkyl hydrocarbons arepermeated into inorganic cementitious compositions in combination with apolar hydrocarbon such as stearyl alcohol which functions similar to awetting agent by enhancing the affinity of the hydrocarbon for thecement and enabling the hydrocarbon to permeate a clay or cement body.In this embodiment, the alkyl hydrocarbon not only conveys its thermalstorage capacity to the body but may also water-proof it.

In accordance with another embodiment of the invention, the alkylhydrocarbon is incorporated into plastic or rubber carriers, with orwithout crosslinking. These composites can be incorporated as granulesor pellets into hydraulic cementitious products or used to make floortiles, wall coverings and the like. Additional thermal storage capacityis gained using crystalline rubber carriers that melt in the same or adifferent temperature range as the alkyl hydrocarbons and exhibit asignificant heat of fusion.

A further embodiment of the present invention resides in polymericcompositions and, more particularly, elastomeric compositions containingcrystalline alkyl hydrocarbon useful in forming moldings, sheets, films,rods, fibers, as well as pellets. These compositions can be designed tobe useful in the manufacture of flooring, tiles and wall panels havingexcellent thermal storage capability.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained by reference to the accompanyingdrawings wherein:

FIG. 1 is a differential scanning calorimetry curve for the cementitiouscomposition of Example 1.

FIG. 2 is a differential scanning calorimetry curve for the polymericcomposition of Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, crystalline alkyl hydrocarbonscontaining 14 or more carbon atoms are incorporated into matrixmaterials where they function as phase change materials.

A number of commercially available waxes with melting points up to about95° C. are useful as phase change materials in the present inventionincluding Shellwax 100 (mp 42°-44° C.), Shellwax 120 (mp 44°-47° C.),Shellwax 200 (mp 52°-55° C.), Shellwax 300 (mp 60°-65° C.), Boron R-152(mp 65° C.), Union SR-143 (mp about 61° C.), Witco 128 (mp about 53°C.), Witco LLN (mp 40° C.), Witco 45A (mp 31° C.), Witco K-61 (mp 24°C.), Witco K-051 (mp 17° C.,), Witco 85010-1 (mp 7° C.), Aristowax 143(mp 34°-61° C.), and Paraffin 150 (mp about 61° C.). These waxes haveheats of fusion greater than 30 cal/g and, by comparison to other phasechange materials, they are inexpensive--many of them costing as littleas 28 U.S. cents per pound when purchased in tank car quantities. Thewaxes can be used alone or in combination. For example, higher meltingcommercial paraffin waxes such as Shell 100 (mp 42° C.), Shellwax 120(mp 44°-47° C.), Shellwax 200 (mp 52°-55° C.), Witco 128 (mp 53° C.),Paraffin 150 (mp 61° C.), can be blended with lower melting C₁₆ (mp 10°C.) and C₁₈ (mp 28° C.) crystalline hydrocarbons to produce phase changematerials with intermediate melting temperatures and these can beincorporated into structures materials as described above.

A preferred group of waxes for use in the present invention are mixturesof crystalline alkyl hydrocarbons in which the melting points of theindividual constitutents fall within a range of about 0° to 95° C. andmore preferably 5° to 60° C. If the difference in melting points of thewaxes making up the mixture is greater than about 20° C. the blend willexhibit two distinct melting points and, hence, possess two heats offusion.

A particularly preferred class of waxes useful in the present inventioncontain a blend of alkyl hydrocarbons and are obtained at low cost asbyproducts of petroleum refining. Because they are inexpensive, they canbe incorporated into building materials at minimal additional expenseand, at the same time, provide high savings in terms of reduced energycosts. The preferred blends for passive heating have a melting point inthe range of 24° to 32° C. Preferred blends for passive cool store havea melting point in the range of 28° to 24° C. In many applications, theblends will be relied upon for heating and cooling. A blend melting andfreezing at 23° to 25° C. can be used as a thermal mass throughout abuilding for heating and cooling. A particularly preferred blend isavailable from Witco Chemical Corporation under the designation K-61.This wax has a melting point of 24° C. and a freezing point of 19.8° C.(by differential scanning calorimetry at 10° C./min. rate of heating andcooling). Chromatographic analysis of K-61 shows that it principallycontains normal paraffins of 16 to 21 carbon atoms with major fractionsconsisting of 17, 18, 19 and 20 carbon atoms.

Thermal energy storage data for five products obtained from WitcoChemical Corporation are shown in the following table which shows thatblends having melting and freezing temperatures which cover the enirerange that is deemed to be of interest for solar passive heating andcooling are available.

    ______________________________________                                                   Tm   Tc      Tm-Tc   Hf     Hc                                                °C.                                                                         °C.                                                                            °C.                                                                            cal/gm cal/gm                                 ______________________________________                                        1. WITCO LLN 40.0   34.7    5.3   51.1   49.2                                 2. WITCO 45-A                                                                              31.4   26.3    5.1   41.2   40.0                                 3. WTTCO K-61                                                                              24.0   19.8    5.2   48.4   47.8                                 4. WITCO K-51                                                                              17.4   12.3    5.1   47.6   11.2                                 5. WITCO 85010-1                                                                            7.6    4.0    3.6   30.4   31.0                                 ______________________________________                                    

Another important consideration in the selection of the alkylhydrocarbons used in the present invention is their tendency forsupercooling or superheating. It is desirable to use alkyl hydrocarbonswhich show little or no supercooling even when cooled at rapid ratessuch as 10° C./min. In any case, the difference in observed melting andfreezing temperatures due to supercooling or superheating is preferablyless than 10° C. More preferably this difference is less than 5° C. andmost preferably less than about 3° C.

In addition to providing blends of alkyl hydrocarbons which exhibitphase change characteristics which are intermediate or approximately theaverage of the individual phase change materials making up the blend, itis also possible to provide blends which exhibit two or more distinctphase changes. Such blends are useful in applications where the phasechange material is relied upon to conserve heat in the winter andconsume cool in the summer. For this embodiment of the invention thedifference in the melting points of the phase change materials should beat least 15° C. Typical examples of such dual temperatures blends is ablend which freezes at 15° C. and melts at 35° C. on heating. Manywaxes, as commercially obtained, are not preferred for use in passiveenergy storage systems as used in climate control because their meltingpoint is too high. Consequently, in accordance with the invention, thesematerials may be combined with crystalline alkyl hydrocarbons having14-18 carbon atoms and, more specifically, 14, 16, or 18 carbon atoms inorder to bring the melting point of the blend within the range of 16° to42° C.

Stearic acid esters are also useful phase change materials. Examples ofuseful stearic acid esters include methyl stearate, ethyl stearate,propyl stearate, butyl stearate, etc. Butyl stearate changes phasesharply at about 23° C. and can be permeated into crosslinkedpolyolefins and percolated into plasterboard.

A particularly desirable embodiment of the present invention utilizesflame-resistant halogenated hydrocarbons and, more particularly,flame-resistant crystalline chlorinated hydrocarbons for flameretardancy. Typical examples of flame-resistant hydrocarbons arehalogenated hydrocarbons such as chlorinated, brominated or fluorinatedhydrocarbons. Representative examples include Chlorowax 80S, availablefrom Diamond Shamrock Corp. Other halogenated hydrocarbon (which are notphase change materials) can also be used, several of which are availablefrom Ethyl Corporation. Included among them are tetrabromophthalicanhydride, tetrabromobisphenol A, and decabromodiphenyl oxide.

A particularly useful flame-resistant hydrocarbon is a brominatedhydrocarbon which is miscible in the phase change material. Miscibilityis particularly important when permeating the flame-resistanthydrocarbon into already formed plasterboard along with the phase changematerial. Examples of brominated hydrocarbons which are miscible in thephase change material are brominated alkanes, and more particularly,brominated cycloalkylalkanes such as dibromoethyldibromocyclohexanewhich is available as Saytex BCL-462 from the Ethyl Corporation.

The flame resistant hydrocarbon is preferably incorporated into thephase change material in a concentration which provides aself-extinguishing product. In the case of Saytex BCL-462amounts as lowas 10% by weight based on the phase change material are sufficient forthis purpose.

Halogenated hydrocarbons are preferably used in combination withconventional flame-resistant fillers such as antimony oxide and otherpolyvalent metal oxides. The weight ratio of halogenated hydrocarbon tooxide may vary, but it is typically about 1:1 to 3:1. Flame-resistantwax formulations have previously been added to polymers to render themself-extinguishing. Wax formulations used for this purpose may also beuseful as flame-resistant phase change materials in accordance with thepresent invention.

Another useful fire retardant is a halogenated phosphate. Particularlyuseful flame-resistant halogenated phosphates are chlorinated phosphatessuch as tri(beta-chloroisopropyl) phosphate which is commerciallyavailable under the designation FYROL PCF from Staffer Chemical Company,Specialty Chemical Division and tri(beta-chloroethyl)phosphate which iscommercially available under the designation PHOSGARD C-22R fromMonsanto Chemical Company. Although insoluble in the phase changematerial, tri(beta-chloroisopropyl) phosphate can be dispersed in thephase change material.

It has been found that alkyl hydrocarbons are compatible with bothcementitious and polymeric materials and, as such, they can beincorporated into these materials and used in the building trade toprovide structures having desirable thermal energy storagecharacteristics.

The inorganic cementitious compositions of the present invention includean inorganic cementitious material as a rigid matrix-forming materialTypical examples of useful cementitious materials are hydraulic cements,gypsum, plaster of Paris, lime, etc. Portland cement is by far the mostwidely hydraulic cement. Portland cements are ordinarily used forconstruction purposes. Types I, II, III, IV, and V may be used. Whitecements, air entrained cements, high alumina cements, masonry cementscan also be used.

Concretes are mixtures of hydraulic cements and aggregates. Typicalaggregates include coarse aggregates such as gravel, granite, limestone,quartz, etc., as well as so-called fine aggregates such as sand and flyash. Conventional hydraulic cement concretes, e.g., Portand cementconcretes, employ major amounts (e.g., about 50 to 75% by volume) ofsuch aggregates in the set product. These cements and concretes fallwithin the term "inorganic cementitious material" as it is used herein.

The inorganic cementitious compositions of the present invention alsoinclude concrete and plaster compositions useful in the manufacture ofpre-formed materials such as concrete blocks, dry wall, and the like aswell as in forming poured concrete structures such as used in formingthe walls, floors, floor pads and partitions of buildings. In addition,the compositions of the present invention also include compositionsuseful in road, runway and bridge deck construction where icing can beprevented by incorporation of the phase change material for thermalenergy storage during the day, and release during the night to preventfreezing of water on the surface.

Alkyl hydrocarbons can be incorporated into inorganic cementitiouscompositions directly by blending the hydrocarbon with the othercomponents of the cement or concrete prior to shaping the compositionsand allowing them to harden. Another method that can be used to greatadvantage is to permeate pre-formed and hardened porous buildingmaterials with the alkyl hydrocarbons. Various concrete, stone-like, orclay based on elements such as dry wall, cured cement products, bricks,and concrete blocks can be permeated with an alkyl hydrocarbon in thismanner.

Infiltration is especially adapted for retrofitting applications. Toinfiltrate pre-formed building materials it is generally necessary toheat the material to a temperature in excess of the melting point of thealkyl hydrocarbon. Of course, in some applications it may not benecessary to actually penetrate the underlying substrate with the alkylhydrocarbon. Rather, the alkyl hydrocarbon composition can simply becoated on the surface layer of the substrate such that it penetratesinto the surface.

The infiltration with C-18 alkyl hydrocarbon can be used to treat andsaltproof, existing highway bridge decks or airport runways to preventthe deterioration caused by salt-induced corrosion of the bridge'sreinforcing steel rods. If the alkyl hydrocarbon is selected to melt andfreeze just above 0° C., the safety hazard, in the snow belt, where thebridge deck freezes before the rest of the highway can simultaneously bereduced or eliminated.

When incorporated into inorganic cementitious compositions by directblending or by permeation, the alkyl hydrocarbons are preferably used incombination with a polar hydrocarbon which functions similar to awetting agent by enhancing the affinity of the alkyl hydrocarbon for thecement and/or lowering its surface tension. In this case the alkylhydrocarbon permeates the concrete and, in addition to functioning as aphase change material, also functions in waterproofing the concrete.

Representative examples of useful polar hydrocarbons include long chain(i.e., having more than 12 carbon atoms) fatty acids and alcohols suchas stearic acid, stearyl alcohol and poor waxes such as montan wax orhydrogenated tallow. The polar hydrocarbon used is also a phase changematerial and thus may be used in amounts up to 100 parts per 100 partsof alkyl hydrocarbon and preferably about 1 to 25 parts per 100 partsalkyl hydrocarbon. The alkyl hydrocarbon migrates throughout theconcrete, and to the surface whereby it seals the concrete and rendersit waterproof.

It has been found that directly incorporating alkyl hydrocarbons intocement or concrete compositions prior to hardening tends to reduce thestrength (not the setting time) of the set concrete. The alkylhydrocarbon is lubricative and reduces the amount of adhesion of thecement to the sand and aggregate that can occur in the concrete matrix.It is generally not desirable to use more than about 5% dry weight alkylhydrocarbon in a concrete composition. However, if the amount ofaggregate in the composition is reduced or the aggregate is completelyeliminated, approximately 10% alkyl hydrocarbon may be added. On theother hand, in gypsum, plaster of paris, or dry wall compositions,between 10 and 20% by weight of the alkyl hydrocarbon may be added inthe wet mix.

It has also been found that the amount of alkyl hydrocarbon incorporatedinto inorganic cementitious compositions such as Portland cementcompositions and the like can also be increased if the alkyl hydrocarbonis used in combination with a highly absorptive filler such as a finelydivided silica (e.g., CAB-O-SIL or HiSil). It has been found thatpre-mixing the alkyl hydrocarbon with such a highly absorptive filler,the hydrocarbon resides in the filler and detracts less from thestrength of the concrete or cement composition.

There is no lower limit on the amount of alkyl hydrocarbon used in thecomposition since theoretically any amount will provide some thermalstorage benefit. Typically, the compositions of the present inventioncontain at least 1% of the crystalline alkyl hydrocarbon.

As previously disclosed, the alkyl hydrocarbons maybe used incombination with other halogenated hydrocarbons and a polyvalent metaloxide to impart flame retardancy to the composition. If the polyvalentmetal oxide is mixed directly with the alkyl hydrocarbon and permeatedinto a concrete block, brick, or the like, the porous network of theblock often strains the oxide from the wax composition. Consequently,when infiltration concrete and clay structures with alkyl hydrocarbons,it has been found desirable to pre-mix metal oxide with the concretecomposition and to permeate the hardened concrete product with thehalogenated wax-containing alkyl hydrocarbon.

Because there is a tendency for alkyl hydrocarbons to detract from thephysical properties of set concrete compositions, it may be desirable toincorporate the hydrocarbon in the cement compositions in one of thepolymeric or wax compositions described below in the form of a pellet orgranule ranging from about 0.25 to 3.0 mm in particle size.

Pellets or granules can be produced by incorporating the alkylhydrocarbon in a polymer, and grinding or cutting the polymer. For usein cementitious compositions, the polymeric compositions need not becross-linked since the thermal form stability of the pellet is notimportant. In this case, the cementitious composition can include up to50% by weight of the pellets or granule containing the hydrocarbon phasechange material. To increase the amount of alkyl hydrocarbonincorporated or imbibed into the pellet and to hold it in the pellet itis often desirable to include the aforementioned absorptive silicafiller in the pellet.

In accordance with one embodiment of the invention, pellets are formedusing hard waxes instead of polymers. The waxes may be crystalline ornon-crystalline. When they are crystalline, depending upon theconditions at which they are used, their heat of fusion may contributeto the thermal storage characteristics of the pellet. This isparticularly useful in active thermal energy storage where highertemperatures are used.

Representative examples of hard waxes which are useful in the presentinvention include Shellwax 300, a product of Shell Oil Company,Chlorowax 70S, stearic acid, and high melting mcirocrystalline waxes(e.g., Petrolite waxes available from Barco Products). These waxes arecharacterized in that they have a melting point greater than 50° C. anda penetration hardness as measured by ASTM D 1321-61T less than about10.

The cementitious compositions of the present invention can be designedfor use in various passive thermal storage applications by appropriatelyselecting the melting point of the alkyl hydrocarbons. Alkylhydrocarbons which melt in the range of about 16° to 42° C. are used inpassive solar heating such as in the building materials and structurespreviously mentioned. For bridge deck or roadway deicing, alkylhydrocarbons which melt at about 5° to 15° C. are preferably used.

In accordance with the present invention, alkyl hydrocarbons can also beincorporated into thermosetting or thermoplastic, elastomeric ornon-elastomeric polymeric materials to form wall coverings, floorcoverings or the aforementioned pellets. Included within the scope ofthe term "polymeric materials" are natural and synthetic rubbers. Thepolymeric material must be compatible with the alkyl hydrocarbons suchthat the alkyl hydrocarbon can be incorporated into the polymericmaterial and remain dispersed therein upon molding or coating. If thematerials are not sufficiently compatible, the alkyl hydrocarbon will bemore difficult to disperse in the polymer and will be present asdissolved phase and as a phase of dispersed droplets. Whether the alkylhydrocarbon is dissolved or dispersed does not appear to have asignificant effect on the melting and crystallization of the phasechange material.

Crystalline long chain hydrocarbons can be most readily dispersed inless polar or non-polar rubbers or polymers such as natural rubber,butyl rubber, polybutadiene, copoly(butadiene/styrene) andcopoly(ethylene/propylene) (EPDM). They can also be dispersed in polarpolymers such as nylons, polyesters, acrylate rubbers, methacrylaterubbers, polyvinl alcohol, ethylene vinylacetate copolymers, polyvinylacetate, vinyl chloride/vinyl acetate copolymer, Neoprene,butadiene-acrylonitrile rubber, etc. It is also desirable to use flameresistant halogenated polymers such as Neoprene, polyvinyl chloride, andpolyvinylidene chloride.

The polymeric compositions of the present invention can be used in acrosslinked or uncrosslinked form depending one end use and the need forthermal form stability. Crosslinking does not necessarily interfere withthe phase change properties of the crystalline alkyl hydrocarbon.However, it is essential that the polymer compositions not becrosslinked to an extent that the phase change material loses itsability to melt and freeze effectively and results in reduced least offusion.

It is particularly advantageous to incorporate the alkyl hydrocarboninto rubbers and other elastomers having significant crystallinity sothat they can also function as phase change materials. Natural rubberreportedly has phase transitions at -6° and 25° C. Neoprene(polychloroprene) reportedly has a crystalline melting point about 32°C., as is desirable for comfort heating. Other semi-crystalline rubbersinclude some EPDM, and copoly- (ethylene/vinyl acetate) rubbers. Hence,a crystalline matrix rubber containing an alkyl hydrocarbon can provideaugmented thermal energy storage capacity since both parts of thecomposite contribute.

The alkyl hydrocarbon can be incorporated into the aforesaid polymericcompositions in amounts of up to 50% by weight, depending on the natureof the hydrocarbon and the polymer used. Theoretically, there is nolower limit on the amount of phase change that is used since somethermal energy storage benefit (although small) accompanies anyaddition. Usually, the phase change material is used in an amount of atleast 1% by weight.

In forming molded products, the alkyl hydrocarbon can be mixed with thepolymeric material in a conventional manner, e.g., in a Banbury or on aroll mill. Furthermore, conventional plasticizers, fillers, pigments,curing agents, accelerators, etc., can be added to the compositions toadjust their physical properties as desired. It is advantageous to addfillers such as finely divided silica and carbon black to the polymercomposition. They may be added in amounts ranging from about 10 to 100parts per 100 parts of polymer.

The polymeric compositions of the present invention can be compounded inan otherwise conventional manner to provide compositions useful informing rubber floor tiles, flooring and the like.

In accordance with another embodiment of the invention, polymericthermoset foams such as polyurethane, or thermoplastic polystyrene foamsuseful in insulation and other applications may be filled with an alkylhydrocarbon to enhance their insulative capacity in accordance with thepresent invention. Flexible open celled foams can be filled with analkyl hydrocarbon by compressing the foam in a melt of the hydrocarbon,and removing the excess by re-compressing the foam after removing itfrom the melt. Preferred foams are flexible, low density, open cellfoams; however, substantially any foam in which enhanced thermal storagecharacteristics are desired can be impregnated with a phase changematerial in accordance with the present invention.

In accordance with still another embodiment of the invention, pelletsformed in accordance with the present invention are used in active orpassive hybrid thermal storage systems such as pellet bed heat exchangerin which a heat exchange fluid such as air, ethylene glycol, water orthe like is circulated through a pellet bed. In this use the pellets(the carrier polymer) are preferably crosslinked and the alkylhydrocarbon has a melting point in the range of 10° to 65° C. In oneembodiment of the invention black pellets (e.g., containing carbon blackfiller) can be formed and used as a combination collector and storageunit. These pellets can be used in solar water heaters where they absorbsunlight and store energy. In this embodiment a phase change materialhaving a melting point of about 140° F. is used. Similarly, pelletsformed in accordance with the invention can be used in a coffee or teacup to keep the drink warm.

A partial listing of building materials which can be modified toincorporate alkyl hydrocarbons as phase change materials in accordancewith the present invention includes plasterboard, plaster, cementblocks, cement stucco, cement floors, plastic and rubber floor tiles,foams insulation and paints.

The present invention is illustrated in more detail by reference to thefollowing examples.

EXAMPLE 1

A cementitious phase change composition was prepared by addingoctadecane to an aqueous slurry of gypsum in an amount of 10 partsoctadecane per 90 parts gypsum. The composition was allowed to hardenand submitted to differential scanning calorimetry (DSC) analysis. Thetemperature scan rate was 10° C. per minute. The DSC curve is shown inFIG. 1. The figure clearly shows the melting (32.2° C.) andcrystallization (27.4° C.) of octadecane. Thus, the C-18 alkylhydrocarbon retains its advantageous latent heat storage characteristicsin gypsum.

EXAMPLE 2

A rubber composition useful in forming sheets or pellets for passivethermal storage was prepared by compounding 100 parts natural rubber,100 parts octadecane, 1 part stearic acid, 40 parts Cabosil, 2.0 partsSantecure NS, 5.0 parts zinc oxide, 2.5 parts Flexzone, and 2.5 partssulfur. The composition was cured at 350° F. for 30 minutes andsubmitted to DSC analysis. The DSC curve at a temperature scan rate of10° C./Min. is shown in FIG. 2. Melting and crystallization of theoctadecane occurred at 25.8° C. and 18.2° C., respectively. The heat offusion of the octadecane was thus retained.

EXAMPLE 3

The follwing rubber (EPDM) compositions were prepared and cured at 350°F. for 30 minutes. The alkyl hydrocarbons employed in each of thecompositions retained their melting point and heat of fusioncharacteristics.

    ______________________________________                                                    Parts by Weight                                                               1    3      7       5    9    11                                  ______________________________________                                        EPDM          100    100    100   100  100  100                               Shell X-100 Paraffin                                                                        66     66     50    33   33   33                                Wax (Shell Oil Co.)                                                           Silica Filler 50     --     50    50   --   --                                Carbon Black Filler                                                                         --     50     --    --   50   50                                Stearic Acid   5      5      5     5    5    5                                DiCup R (Hercules                                                                            3      3      3     3    3    3                                Chemical Co., vulcan-                                                         izing agent)                                                                  Octadecane    --     --     16    33   --   --                                Octadecane (technical                                                                       --     --     --    --   33   --                                grade)                                                                        Hexadecane    --     --     --    --   --   33                                ______________________________________                                    

EXAMPLE 4

Twelve 2"×2" squares of plasterboard were dried in a vacuum dessicatorovernight and then weighed and labeled. Separate melt mixed percolatingbaths were prepared containing LLN/BCL-462/stearic acid in the ratios of85/10/5, 80/15/5 and 75/20/5. Another series was prepared using45A/BCL-462 /stearic acid in the same ratios. The blends were weighedinto metal beakers and heated to 80° C. Duplicate plasterboard sampleswere immersed in each blend for ten minutes. After ten minutes in thebath, the samples were immediately removed and weighed to calculate thepercent phase change material (PCM) absorbed which is listed in Table 1for each sample.

                  TABLE I                                                         ______________________________________                                        WITCO 45A/BCL-462/STEARIC ACID                                                PICKUP IN PLASTERBOARD PERCOLATED                                             WITH THE FIRE RETARDANT POSITIONS                                                                   Dry Weight Final                                        Sample #   Ratio      % PCM Pickup                                            ______________________________________                                        45 A/BCL 462/Stearic Acid                                                     1          85/10/5    33.8                                                    2          85/10/5    34.13                                                   3          80/15/5    35.08                                                   4          80/15/5    34.09                                                   5          75/20/5    33.91                                                   6          75/20/5    33.02                                                   Control 1  95/0/5     32.99                                                   Control 2  95/0/5     32.75                                                   LLN/BCL 462/Stearic Acid                                                      7          85/10/5    34.38                                                   8          85/10/5    34.02                                                   9          80/15/5    34.80                                                   10         80/15/5    34.69                                                   11         75/20/5    34.96                                                   12         75/20/5    34.22                                                   Control 1  95/0/5     35.75                                                   Control 2  95/0/5     34.96                                                   ______________________________________                                    

The paper cover was completely removed from one of the squares in eachgroup. Each sample was mounted horizontally in a hood and ignited forten seconds with a Bunsen burner. Table 2 is a compilation of the fireretardant test data.

                                      TABLE 2                                     __________________________________________________________________________    FIRE RETARDANCE TESTS OF PERCOLATED PLASTERBOARD                                         Ignite in                                                                          Time to                                                                             Time to Ignite                                                                        Flame                                                                              Time to                                    Sample #                                                                            Ratio                                                                              10 sec                                                                             Extinguish                                                                          and Stay Lit                                                                          Traveled                                                                           Extinguish                                                                          Smoke                                __________________________________________________________________________    45A/BCL 462/Stearic Acid                                                      1     85/10/5                                                                            Yes  Immed.                                                                              30 sec  Yes  375 sec                                                                             wh & blk                             2     85/10/5                                                                            Yes  Immed.                                                                              29      Yes  390   wh & blk                             3     80/15/5                                                                            Yes  Immed.                                                                              26      Yes  341   wh & blk                             4     80/15/5                                                                            Yes  Immed.                                                                              25      Yes  201   wh & blk                             5     75/20/5                                                                            Yes  Immed.                                                                              30      Yes  160   wh & blk                             6     75/20/5                                                                            Yes  Immed.                                                                              30      Yes  130   wh & blk                             Control 1                                                                           95/0/5                                                                             Yes  10 min.                                                                             10      Yes  10 min.                                                                             wh & blk                             Control 2                                                                           95/0/5                                                                             Yes  10 min.                                                                             10      Yes  10 min.                                                                             wh & blk                             LLN/BCL 462/Stearic Acid                                                      7     85/10/5                                                                            Yes  Immed.                                                                              12 sec  Yes  323 sec                                                                             wh & blk                             8     85/10/5                                                                            No   Immed.                                                                              15      Yes  272   wh & blk                             9     80/15/5                                                                            Yes  Immed.                                                                              20      Yes  237   wh & blk                             10    80/15/5                                                                            No   Immed.                                                                              25      Yes  196   wh & blk                             11    75/20/5                                                                            Yes  Immed.                                                                              30      Yes  155   wh & blk                             12    75/20/5                                                                            No   Immed.                                                                              36      Yes  58    wh & blk                             Control 1                                                                           95/0/5                                                                             Yes  10 min.                                                                             10      Yes  10 min.                                                                             wh & blk                             Control 2                                                                           95/0/5                                                                             Yes  10 min                                                                              10      Yes  10 min.                                                                             wh & blk                             __________________________________________________________________________     NOTE                                                                          Evennumbered samples had paper covers removed                            

Controls were included containing LLN/stearic acid and 45A/stearic acidin the ration of 95/5.

Having described the invention in detail and by reference to specificembodiments thereof, it will be apparent that numerous modifications andvariation are possible without departing from the scope of the followingclaims.

What is claimed is:
 1. A composite useful in thermal energy storagecomprising a matrix having incorporated therein a phase change material,said phase change material being a crystalline, .[.straight.]..Iadd.long .Iaddend.chain, alkyl hydrocarbon having 14 or more carbonatoms and a heat of fusion greater than 30 cal/g., said composite alsocomprising a flame retarding agent selected from the group consisting ofhalogenated hydrocarbons and halogenated phosphates.
 2. The composite ofclaim 1 wherein said matrix material is an inorganic cementitiousmaterial.
 3. The composite of claim 2 wherein said inorganiccementitious material is selected from the group consisting of hydraulic.[.cements, gypsum, and concrete..]..Iadd.cements andgypsum..]..Iaddend.
 4. The composite of claim 3 wherein said phasechange material is incorporated into said matrix material in the form ofa pellet.
 5. The composite of claim 4 wherein said pellet comprises amatrix of a hard wax having a melting point greater than 50° C. and apenetration hardness less than 10 containing said phase change material.6. The composite of claim 3 wherein said phase change material ispre-mixed with a highly absorptive filler before being introduced tosaid matrix material.
 7. The composite of claim 1 wherein said flameretarding agent also includes a polyvalent metal oxide.
 8. The compositeof claim 2 wherein said composite is formed by infiltrating said matrixmaterial with said phase change material in combination a wetting agent.9. The composite of claim 8 wherein said wetting agent is stearic acidor stearyl alcohol. .[.10. The composite of claim 1 wherein said alkylhydrocarbon is selected from the group consisting of Shellwax 100,Shellwax 120, Shellwax 200, Shellwax 300, Boron R-152, Union SR-143,Witco 128, Witco LLN, Witco 45A, Witco K-61, Witco K-51, Witco 85010-1,Aristowax 143 and Paraffin 150..].
 11. The composite of claim 2 whereinsaid alkyl hydrocarbon is a blend of normal alkyl hydrocarbonscontaining 16 to 20 carbon atoms.
 12. The composite of claim 1 whereinsaid halogenated hydrocarbon is selected from the group consisting of.[.Chlorowax 70-S,.]. tetrabromophthalic anhydride, tetrabromobisphenolA, and decarbomodiphenyl oxide; and said polyvalent metal oxide isantimony oxide, the weight ratio of said halogenated hydrocarbon to saidantimony oxide being about 1:1 to 3:1.
 13. A composite of claim 1wherein said composite is a bridge deck.
 14. A composite useful inthermal energy storage comprising a matrix material having incorporatedtherein a phase change material, said matrix material being plasterboardand said phase change material being a crystalline, .[.straight.]..Iadd.long .Iaddend.chain, alkyl hydrocarbon having 14 or more carbonatoms and a heat of fusion greater than 30 cal/g., said plasterboardalso comprising a flane retardant agent incorporated therein said flameretarding agent being selected from the group consisting halogenatedhydrocarbons and halogenated phosphates.
 15. A composite useful inthermal energy storage comprising a matrix material having incorporatedtherein a phase change material and a flame retarding agent, said phasechange material being a crystalline .[.straight.]. .Iadd.long.Iaddend.chain alkyl hydrocarbon having 14 or more carbon atoms and aheat of fusion greater than 30 cal/g and said flame retarding agentbeing a brominated hydrocarbon which is miscible in said phase changematerial.
 16. The composite of claim 15 wherein said brominatedhydrocarbon is a brominated cycloalkylalkanes. The composite of claim 16wherein said brominated cycloalkylalkane isdibromoethyldibromocyclohexane.
 18. The composite of claim 1 whereinsaid flame retarding agent is a flame retarding agent selected from thegroup consisting of tri(beta-chloroisopropyl) phosphate andtri(beta-chloroethyl)phosphate. .Iadd.19. A method of thermal energystorage comprising providing a composite in thermally stable form andformed of a first material and a second material which is different fromsaid first material, and which has a melting point less than said firstmaterial, but which is compatible with said first material, said firstmaterial comprising an inorganic cementitious matrix which serves as acontainment means for said second material, said second materialcomprising a crystalline alkyl hydrocarbon material containing 14 ormore carbon atoms or mixtures thereof and having a heat of fusiongreater than about 30 cal/g, said second material being contained withinthe matrix of said first material, and subjecting said composite tochanges in temperature whereby said composite either conserves heat orcool. .Iaddend. .Iadd.20. The method of claim 19 wherein said inorganiccementitious matrix comprises a cementitious material selected from thegroup consisting of hydraulic cements and gypsum. .Iaddend. .Iadd.21.The method of claim 20 wherein said inorganic cementitious matrix is inthe form of a dry wall or a cured cement product. .Iaddend. .Iadd.22.The method of claim 21 wherein said composite is formed by infiltratingsaid inorganic cementitious matrix with neat crystalline alkylhydrocarbon. .Iaddend. .Iadd.23. The method of claim 23 wherein saidcrystalline alkyl hydrocarbon is used in combination with a wettingagent. .Iaddend. .Iadd.24. The method of claim 20 wherein neatcrystalline alkyl hydrocarbon is incorporated directly into saidinorganic cementitious matrix by wet or dry mixing. .Iaddend. .Iadd.25.The method of claim 25 wherein said crystalline alkyl hydrocarbon isused in combination with a wetting agent. .Iaddend. .Iadd.26. The methodof claim 19 wherein said phase change material comprises from 1 % to 20%by weight of said composition. .Iaddend.